linux-kernel - Re: [PATCH 02/12] selftests/x86: Add check_initial_reg

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Message-ID: <20151208095455.GC27180@pd.tnic>
Date:	Tue, 8 Dec 2015 10:54:55 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Brian Gerst <brgerst@...il.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 02/12] selftests/x86: Add check_initial_reg_state

On Mon, Dec 07, 2015 at 01:51:27PM -0800, Andy Lutomirski wrote:
> This checks that ELF binaries are started with an appropriately
> blank register state.
> 
> (There's currently a nasty special case in the entry asm to arrange
>  for this.  I'm planning on removing the special case, and this will
>  help make sure I don't break it.)
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  tools/testing/selftests/x86/Makefile               |   8 +-
>  .../selftests/x86/check_initial_reg_state.c        | 108 +++++++++++++++++++++
>  2 files changed, 115 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/x86/check_initial_reg_state.c
> 
> diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
> index a460fe7c5365..b82409421fa6 100644
> --- a/tools/testing/selftests/x86/Makefile
> +++ b/tools/testing/selftests/x86/Makefile
> @@ -4,7 +4,7 @@ include ../lib.mk
>  
>  .PHONY: all all_32 all_64 warn_32bit_failure clean
>  
> -TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs ldt_gdt syscall_nt ptrace_syscall
> +TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs ldt_gdt syscall_nt ptrace_syscall check_initial_reg_state
>  TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault sigreturn test_syscall_vdso unwind_vdso
>  
>  TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
> @@ -63,3 +63,9 @@ endif
>  sysret_ss_attrs_64: thunks.S
>  ptrace_syscall_32: raw_syscall_helper_32.S
>  test_syscall_vdso_32: thunks_32.S
> +
> +# check_initial_reg_state is special: it needs a custom entry, and it
> +# needs to be static so that its interpreter doesn't destroy its initial
> +# state.
> +check_initial_reg_state_32: CFLAGS += -Wl,-ereal_start -static
> +check_initial_reg_state_64: CFLAGS += -Wl,-ereal_start -static
> diff --git a/tools/testing/selftests/x86/check_initial_reg_state.c b/tools/testing/selftests/x86/check_initial_reg_state.c
> new file mode 100644
> index 000000000000..0cb565f7786d
> --- /dev/null
> +++ b/tools/testing/selftests/x86/check_initial_reg_state.c
> @@ -0,0 +1,108 @@
> +/*
> + * check_initial_reg_state.c - check that execve sets the correct state
> + * Copyright (c) 2014-2015 Andrew Lutomirski
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +
> +#define _GNU_SOURCE
> +
> +#include <stdio.h>
> +
> +unsigned long ax, bx, cx, dx, si, di, bp, sp, flags;
> +unsigned long r8, r9, r10, r11, r12, r13, r14, r15;
> +
> +asm (".pushsection .text\n\t"

WARNING: please, no spaces at the start of a line
#82: FILE: tools/testing/selftests/x86/check_initial_reg_state.c:23:
+     ".type real_start, @function\n\t"$

Something trampled over the preceding tabs in that whole asm().

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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